On the basis of our own results and data generated by others, we have concluded that dendritic cells (DCs) are a key element involved in dictating the nature of the immune response generated by virus infection. In particular, our data demonstrate that influenza or Sendai virus infected DCs undergo maturational events associated with increased expression of costimulatory molecules and MHC and release of key cytokines leading to Th1 immune responses. We hypothesize that these maturational changes in DCs are closely linked to virus replication associated with the production of triggering molecules such as dsRNA and activation of the interferon pathway. Unfortunately, there is little data on the direct effect of virus on maturation of DC and even less evidence related to in vivo collected cells. Thus, we propose to investigate the roles of adapter proteins and transcription factors chosen based on results of DC maturation initiated through toll like receptors (TLRs). Additionally, our data suggest involvement of mediator such as IRF3 known to be involved in the induction of interferon. We propose two approaches to elucidate the key factors. In the first, we will utilize mice in which genes involved in producing elements that are suspected of playing a key role have been deleted. Thus, we will employ mice in which genes for IRF-3, MyD88, type 1 interferon receptor and STAT1 have been deleted. Our second approach will use a reverse genetics system with Sendai Cantell virus to create recombinant viruses in which genes associated with DC maturation or inhibition of interferon induction have been introduced. These genes will include genetics elements of viruses known to have anti-interferon activity. They will also include dominant negative mutants of important genetic elements in the interferon pathway or TLR pathways. The value of this system is that Sendai virus is a natural pathogen of mice and the particular strain that we will employ is the most potent virus we have tested in the induction of DC maturation. In addition we propose to further investigate RSV, which in preliminary observations produces an unusual pattern of DC maturation and results in an immune response with unusual characteristics. Thus, having examined only a limited array of viruses, we are aware that different viruses exhibit different effects on DC maturation and result in different types of immune responses. [unreadable] [unreadable]